This disclosure relates generally to ion implanters, and more specifically to a high voltage insulator that prevents instability in an ion implanter due to triple junction breakdown.
A high voltage insulator is typically used in an ion implanter in locations along the beamline where there is a need for high voltage. For example, high voltage is necessary to extract an ion beam from an ion source. In particular, a high voltage insulator is used with an extraction system that receives the ion beam from the ion source and accelerates positively charged ions from within the beam as it leaves the source. Other locations where a high voltage insulator can be used in the beamline include an electrostatic lens that focuses the ion beam and an acceleration or deceleration stage that accelerates or decelerates the ion beam to a desired energy, respectively.
Current high voltage insulator designs that are in use with a typical ion implanter are subject to triple junction breakdowns that lead to instability (e.g., high voltage instability, ion beam instability) and eventually failure of the implanter. A triple junction region in a high voltage insulator is the junction or region where three volumes having different electrical characteristics come together and thus the local electric field at the triple junction region is intensified due to the step change of the electrical characteristics at the triple junction region. The three volumes typically include a dielectric (e.g., insulator) that holds off high voltage, metal electrodes (e.g., metallic conductor), and a vacuum in the interior of the beamline. The dielectric and the metallic conductor together form the vacuum vessel to transport the ion beam and protect it from atmospheric pressure. An O-ring is sandwiched between the dielectric and the metallic conductor to provide a vacuum seal from atmospheric pressure. In addition, the O-ring allows the metallic conductor to be disassembled from the dielectric during the maintenance of the high voltage insulator. A vacuum seal interface gap is produced between the dielectric and the metallic conductor. The vacuum seal interface gap is a narrow or microscopic space containing many voids. The vacuum seal interface gap is located at exactly the same place where a triple junction region is located.
During operation of the high voltage insulator, these voids formed in the vacuum seal interface gap or triple junction region not only have intensified local electric fields but also have poor vacuum pressure that promote electric discharge which makes the vacuum pressure even worse, triggering a secondary ionization. Eventually the secondary ionization will trigger a breakdown in a triple junction region that propagates along an inner surface of the dielectric until it reaches the opposite electrode and shorts out the power supply, resulting in ion implanter failure.
Therefore, it is desirable to develop a high voltage insulator that can prevent triple junction breakdown that causes instability in an ion implanter.